This invention relates generally to a ventilation system having a damper blade rotatably mounted within a supply air duct provided to deliver conditioned air to an enclosure, and more particularly to a control for such a damper blade.
Many multi-room structures, for example office buildings and schools, constructed during the past several years include air conditioning systems which deliver either relatively warm or cool, conditioned air from a central source thereof to each of the enclosures or rooms in the building. Typically, one or more supply air ducts are employed to transmit or conduct the conditioned air to each enclosure. Often, each supply air duct includes a damper assembly or similar mechanism having a movable damper blade to regulate the flow of air through the supply air duct. Movement of the damper blade may be responsive to changes in the pressure of the air passing through the supply air duct and/or changes in the temperature of the enclosure served thereby.
It is frequently desirable to constantly deliver at least a minimum amount of air to an enclosure regardless of the temperature thereof to insure a continuous circulation of air through the enclosure. A continuous, even though minimal, flow of air may prevent, for example, the accumulation of smoke or odors or the development of localized areas of stagnated air in the enclosure. Also, it is often advantageous to limit the maximum air flow into a room to prevent or minimize, as examples, undesirable noise, drafts, or localized cool areas within the room. Moreover, due to a number of reasons such as size, location, and use, different rooms often have different preferred maximum and minimum air circulation rates. For these reasons, damper assemblies commonly have controls to maintain the damper blade of the assembly between adjustable minimum and maximum air flow positions, independent of the thermostatic and pressure controls for the blade. The minimum and maximum positions of a particular damper blade are adjusted to fit the needs of the specific enclosure or room with which the damper blade is eventually associated. Recently, attention has been directed toward employing an electric motor to move a damper blade of a damper assembly between minimum and maximum air flow positions. Prior art arrangements for moving a damper blade by means of an electric motor have been somewhat inefficient or expensive, however, often, for example, supplying current to the motor even though the damper blade is at a maximum position and the motor is stalled.